Hello Kevin,
Nice to see you building something. It's an important step, after studying and
thinking some, to verify your design.
A first approximation of thrust is Pc * At (chamber pressure * throat area) -
increase PC or At and thrust increases.
Later refined by Cf (Thrust coefficient which accounts for most of the fiddly
bits).
Best book would be Rocket Propulsion Elements by Sutton, 3rd edition or higher,
often available on eBay.
When testing, please treat your thrust chamber as a grenade. That is, don't put
anything near it that you don't want punctured by flying metal
For example, don't stand there trying to read the scales while it's thrusting.
:-)
Good luck!
Ed Kelleher
At 05:51 PM 4/17/2023, kevin ward wrote:
Can anyone help with this equation...
More psi in combustion chamber, no matter what, results in more thrust ?
BurnSim says so...
But dad insists NASA knows best and may 1 at the throat is penultimate.
Cutting issues with "supersonic velocities, at the throat, cause problems" he
pointed out a nozzle that had Mach 1 as Max propellant mass flowing, for
longer burn time... Vs less mass at higher velocities for less burn time.
Analogy: water hose at full open creates a little thrust, put a nozzle on it
and hold on... As in a fireman's hose or a high pressure washer. You're only
going to get thrust if you tighten up the throat.
I could see a different analogy that proves me wrong as in with a boat and
it's propeller. There is a point before velocity increases, that if you apply
too much torque, you're going to cavitate. Does that apply in rockets ?
I insist that NASA is limited in acceleration due to what they're sending up;
people, equipment, O-rings that go bang, etc. And the whole point is to
"attain escape velocity as quickly as possible". Another NASA quote
"controlled explosion".
Furthermore, throats and nozzle ends are maximized per the individual rocket.Â
I figure they could go for, instead of steel motor casings, maybe kevlar
wrapped at 15 times psi, yielding a bunch more thrust, if they only sent a
rocket, with no purpose, other than trying 2 attain fastest object ever, other
than light.
I realize the rocket will burn up due to friction, unless properly insulated,
which isn't difficult.
If I just want to send a probe, to the kuiper belt, and wave an aerogel disc,
return and splash into the ocean.... I'll b limited by difficulty in not
destroying the aerogel, but, not NASA's fastest ever rocket, being considered
best velocity.
If you don't know, please instruct me where 2 go... B nice
Lol
Ty 4 your assistance.
P.s. Looking for team members\collaborators
Oh, pic of of M-2270. A little extra kiln coat on exterior to measure variable
temps. Inside casing is generous slathering of kiln coat (100HT). Double
choked nozzle will be additionally .25" kevlar adhered. (Playing safe at
30,000psi, but figure capable of 50,00psi considering my imperfect epoxy to
kevlar fabric ratio.
Using air intake Jets to create gas wedge to alter vector. Passively. No gyros
or otherwise.
Additionally playing with extra metals in the propellant, i.e. rich
fuel\oxidizer mix. some of my fuel won't b onboard, rather scooped up as
accelerating, yielding less propellant mass required.
On Mon, Apr 17, 2023, 2:29 PM Henry Spencer
<<mailto:hspencer@xxxxxxxxxxxxx>hspencer@xxxxxxxxxxxxx> wrote:
On Mon, 17 Apr 2023, Uwe Klein wrote:
A corollary:Â if you think of the first vehicle as a pathfinder rather
than as the main operational moneymaker, it should be sized for easy
manufacturing and operation,
You learn about the target environment.
But scaling effects may turn design decisions upside down.
Yes, you don't necessarily get the main operational moneymaker by just
running the pathfinder's plans through the Enlarge setting on the
photocopier. However, the real plans will also differ significantly from
what you'd have drawn before building and operating the pathfinder. The
purpose of the pathfinder is not to flight-test the technical design of
the operational vehicle, in miniature; it's to give you a better idea of
what that design should look like.
And the technical design of the vehicle is not the only issue. Building a
team that can do a good job on the operational vehicle is part of it too.
So is acquiring credibility as a launch supplier, and figuring out how to
navigate the regulatory process. (Falcon 1 was financially a complete
flop for SpaceX, but it opened doors that were crucial to Falcon 9's
success.)Â Thinking of success in the launch business as purely a
technical problem is a dangerous delusion.
Henry
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